1. Field of Invention
The present invention relates to a hydraulic control system of an automatic transmission for a hybrid vehicle. More particularly, the present invention relates to a hydraulic control system of an automatic transmission for a hybrid vehicle which simplifies structure of a valve body and improves responsiveness by directly controlling hydraulic pressure supplied to friction elements.
2. Description of Related Art
Generally, a hybrid vehicle is a vehicle generates driving torque by efficiently combining two or more different types of power sources. Most hybrid vehicles are provided with an engine generating power by using fuel and an electric motor generating power by electricity.
Cases which greatly enhance fuel economy of a hybrid vehicle are: (1) assisting power of the engine by using the electric motor when the vehicle accelerates or (2) performing optimal driving through automatic shift control. Therefore, the hybrid vehicle can obtain excellent fuel economy compared with a conventional vehicle provided with a gasoline engine and an automatic transmission.
According to such a hybrid vehicle, an engine clutch is disposed at an output of the engine and an automatic transmission including the electric motor is disposed at the rear of the engine clutch. As a result, driving wheels are driven by the power output from the automatic transmission.
In addition, a motor control unit controls electricity of battery supplied to the electric motor, and a hybrid control unit controlling the hybrid vehicle totally is electrically connected to an engine control unit, a transmission control unit, a battery management system, and other devices which a driver directly manipulates so as to receive a current driving condition of the vehicle and controls the motor control unit based thereon.
When initial running, the hybrid vehicle runs at electric vehicle EV mode by torque of the electric motor. After that, if the engine clutch is engaged, the hybrid vehicle runs at HEV mode (motor+engine).
The automatic transmission applied such a hybrid vehicle includes a gear train which is a shift mechanism and a hydraulic control system for selectively operating at least one operating element among operating elements of the gear train according to the driving condition of the vehicle.
In addition, the gear train includes one or more planetary gear sets, and a plurality of friction elements applied to the gear train is selectively operated by hydraulic pressure supplied by the hydraulic control system.
According to a conventional hydraulic control system of an automatic transmission for a hybrid vehicle, hydraulic pressure supplied from a hydraulic pump is indirectly controlled and is supplied to each friction element. Since a pressure control valve including a spool valve is applied to each solenoid valve, hydraulic lines of a valve body are complex and a large number of components are used. Therefore, manufacturing cost may be increased.
Since reducing pressure should be generated so as to control the pressure control valve, control region may be restricted and responsiveness may be slow.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.